This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
This circuit was obtained in a General Electric documentation from the 80's, and can be used as a...
This circuit appears in various parts of this site and this section, with diverse origins. This is from...
November 2016 - The TL3780 ultra-miniature E-switch touch switches can now be obtained from Mouser...